The presence of lactic acid in the cell of an animals muscle tissue is an indication that the

The animal has been performing vigorous activity with an insufficient oxygen availability in its muscles.

Explanation:

Lactic acid is an alpha-hydroxy acid (AHA) that is fundamental in the biochemical processes of the body.

During normal levels of oxygen in the body, the carbohydrates that are present in the body are transformed into water and CO2. On the other hand, when oxygen levels are low, lactic acid is produced.

Therefore, when an animal is performing vigorous exercise and the levels of oxygen in the body are low or insufficient, the muscles begin to respire anaerobically and, instead of CO2 and H2O, lactic acid is produced.

So, the presence of lactic acid in the cell of an animals muscle tissue is an indication that the animal has been performing vigorous activity with an insufficient oxygen availability in its muscles.